1. Technical Field
The present invention relates to fluid distribution face seal connections and, more particularly, to locking devices to prevent relative rotation between compression nuts used to enclose face seal attachments.
2. Discussion of the Prior Art
Face seal mechanical fittings are employed in many industrial and research applications. They provide a quick and convenient way to join tubing in fluid distribution systems. These connections sometimes develop leaks in service due to improper makeup, mechanical action on the connection, especially torquing up stream or down stream, and many other reasons. When the connection loosens, leaks are possible. In many applications, even very small leaks can cause process problems, and in some cases, severe safety hazards. This is especially true in applications involving UHP (Ultra High Purity) gases or hazardous materials.
A number of devices have been developed to minimize the effects of mechanical vibration on these face seals, particularly to prevent the relative rotation between securing nuts that result in loosening of the compression and ultimately in compromise of the connection. Locking wires passing through fine holes drilled in one or both of the compression nuts, then tied together or into surrounding structure afford improvement, but fail to provide a positive mechanical lock and require cumbersome preparation and installation.
Another approach, exemplified by U.S. Pat. No. 5,362,111 (Harbin), incorporates a U-shaped flat spring having a serrated edged aperture formed in one of two facing surfaces, sized to nonrotatably engage the points of a first polygonal compression nut, and a second aperture formed in the second facing surface to engage similarly a second compression nut, with or without a clutching pattern on one aperture. A fluid line nut locking device exemplified by U.S. Pat. No. 5,222,768 (Hofer et al) uses a similar approach with two separate box wrenches sized to engage two compression nuts and locked nonrotatably together with a bolt passing through tabs inwardly extending from the two wrenches toward one another. Each of these devices inconveniently requires disassembly of the compression fitting for removal.
U.S. Pat. No. 5,312,139 (Marks et al) is similar to the Hofer patent with slots formed in each of the box wrenches to permit passage of the fluid line while still affording engagement of the compression nuts to allow the device to be retrofit onto existing fittings without requiring disassembly thereof. Rotational adjustment between the two compression nuts is limited by the engagement surfaces formed between the nut points and flats and those of the corresponding wrench apertures.
Semicircular spring bands, serrated to form gripping surfaces to engage compression nuts are joined by at least one axial bridge or bar to oppose relative nut rotation in U.S. Pat. No. 5,350,201 (Bynum). The resilience required to permit snap fitting of this device over the nuts limits the rigidity of connection necessary for hazardous and ultra high purity fluid connections. None of these prior art locking devices assures a rigid positive non-rotating connection between precisely spaced compression nuts while at the same time allowing assembly and disassembly of the locking members without requiring detachment of the fluid face seal.